Mislanding corrector for color cathode ray tubes

ABSTRACT

A temperature-responsive magnetic device comprising a pair of permanent magnet elements, each partly enclosed in a separate magnetic element that has temperature-responsive variable permeability, is provided for attachment to the wall of a color cathode ray tube to compensate for beam mislanding on the color phosphor screen caused by thermal expansion of a beam selecting mask in the tube. The avoidance of mislanding is necessary to maintain fine color purity of color television images produced by the tube.

United States Patent [191 Machida et al.

[ MISLANDING CORRECTOR FOR COLOR CATHODE RAY TUBES [75] Inventors: Hiromasa Machida, Tokyo; Hiroshi Ichigaya, Toda; Kietsti Iwabuchi, Tagajo, all of Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: Nov. 20, 1973 [21] Appl. No.: 417,591

[30] Foreign Application Priority Data Nov. 20, 1972 Japan 47-l3353 [52] U.S. Cl 313/430, 313/431, 335/217 [51] Int. Cl. HOlj 29/70 [58] Field of Search 313/69 C, 70 C, 75, 76, 313/79, 84, 402, 409, 429, 430, 431;

[56] References Cited UNITED STATES PATENTS 2,972,073 2/196] Clay 313/84 X [4 1 Mar. 25, 1975 Vetake et al. 335/212 Fuse 335/210 X Primary E.\'aminer-Rudolph V. Rolinec Assixranr E.raminerE. R. LaRoche Attorney, Agent, or FirmLewis H. Eslingcr; Alvin Sinderbrand [57] ABSTRACT A temperature-responsive magnetic device comprising a pair of permanent magnet elements, each partly enclosed in a separate magnetic element that has temperature-responsive variable permeability, is provided for attachment to the wall of a color cathode ray tube to compensate for beam mislanding on the color phosphor screen caused by thermal expansion of'a beam selecting mask in the tube. The avoidance of mislanding is necessary to maintain fine color purity of color television images produced by the tube.

8 Claims, 9 Drawing Figures MISLANDING CORRECTOR FOR COLOR CATI-IODE RAY TUBES BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates generally to means for avoiding beam mislanding in a color cathode ray tube having a beam-separating structure and a color phosphor screen, and more particularly to means of compensating for such mislanding caused by temperature variations in the beam-separating structure of the color cathode ray tube.

2. The Prior Art In a conventional color cathode ray tube there is a beamseparating structure in the form of a mask or grille that has a number of small apertures or slits therethrough to allow the electron beams to reach, or land on, only the phosphor elements that emit light of selected colors. In such tubes, heat is generated by the impingement of the electron beams on the beamseparating structure. This heat causes thermal expansion or distortion of the beam-separating structure with the result that the positions of the slits or apertures are shifted relative to the phosphor elements of the screen. This causes the landing positions of the electron beam on the color phosphor screen to shift, and this mislanding of the electron beams, in turn, causes deteriorations in color purity. The mislanding of the electron beam is worse near the periphery of the screen than at the center and is particularly objectionable in the case of wide angle beam scanning tubes.

Several ways have been proposed to compensate for thermally-induced electron beam mislanding. One conventional system is to hold the mask by a bimetallic support to change the position of the mask in the tube relative to the screen in response to temperature change. Another compensating system uses an auxiliary beam deflection coil in addition to the main deflection coil. The current in the auxiliary beam deflection coil is changed in response to the mask temperature to change the electron beam path in order to avoid the mislanding of the electron beams.

However, such conventional systems mentioned above have several drawbacks. The are complicated in construction, they require a number of parts, and they are expensive.

In the corresponding U.S. Pat. Application Ser. No. 329,049, filed Feb. 2, 1973 and assigned to the asignee of the present case, individual permanent magnets have been partially enclosed in magnetic shunt structures that were temperature-responsive in the sense that the permeability of the shunt changed when its temperature changed. As the temperature increased, the permeability decreased. However, these individual magnetic structures produced relatively concentrated fields and the strength of the magnetic fields produced by these structures could not easily be controlled.

Accordingly, an object of this invention is to provide a simplified color cathode ray tube arrangement wherein the magnetic flux to eliminate mislanding of electron beams on the screen of the color cathode ray tube caused by temperature variations in the mask and screen is spread out over a relatively large area by the correcting means located on the funnel portion of the tube.

Still another object of this invention is to provide a color cathode ray tube arrangement in which temperatureinduced mislanding of the electron beams in wide angle tubes is prevented by a temperature-responsive permanent magnetic device of simple construction in which the magnetic field is spread over a large area in a controlled manner.

A further object of this invention is to provide a simple color-purity'correcting means comprising a pair of temperature-responsive permanent magnetic devices for balanced correction of mislanding.

SUMMARY OF THE INVENTION According to this invention, a temperatureresponsive magnetic device is provided in the form of two permanent magnets, such as discs with diametrically opposed north and south poles, each magnet being held by a magnetic shunt the permeability of which changes in response to temperature variation. The shunt-held magnets are joined by a relatively high-permeability member, such as a strap of silicon steel that helps control the flux distribution from the magnets. The resulting two-magnet structure can be attached to the cathode ray tube at a predetermined position between the beam deflection center of the tube and the screen in order to modify the paths of the beams. The extent to which the strap further shunts the fields of the magnets at its ends is a means for controlling the strength of the fields produced by the magnets.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of one example of a temperature-responsive magnetic device employed in a color cathode ray tube temperature compensating structure according to the invention.

FIG. 2 is a cross-sectional view of the device shown in FIG. 1.

FIG. 3 is a side elevational view of a complete temperature-responsive magnetic structure incorporat ing two of the devices shown in FIGS. 1 and 2 according to the invention.

FIG. 4 is a plan view of the structure shown in FIG. 3.

FIG. 5 is a side elevational view similar to FIG. 3 but illustrating magnetic flux distribution in the vicinity of the structure.

FIGS. 6 and 7 illustrate the variation in the magnetic flux field in the vicinity of the magnetic structure as the overlap between the strap and one of the magnetic devices is varied.

FIGS. 8 and 9 show side and rear views of a color cathode ray tube with two magnetic structures according to the invention attached to the funnel portion to correct for beam mislanding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show one embodiment of a temperature-responsive magnetic device 11 used in the magnetic structure of this invention. The device 11 includes a permanent magnet 12 held in a recess in a shunt 13 made of temperature-responsive magnetic material. The permanent magnet 12 may be made of, for example, Ba-ferrite containing BaCO; and Fe O in the ratio of 15:85 by mol% and may be formed as a disc magnetized along its diameter at the pole locations marked N and S. To assist in assembly the disc 12 and the shunt 13, the disc is formed so that its physical shape can be used to indicate the locations of thepoles N and S. For

. example, the disc 12' has one flat section 14 along its edge, and the magnetizing of the disc is always carried out so that the poles N and S have a certain relationship to this edge. The shunt 13 is also provided with flat edge 16 for the same reason.

The temperature-responsive magnetic material of the shunt 13 may be made of MnZn-ferrite and formed as a disc having a recess. The shunt 13 has a magnetic permeability that decreases as the temperature increases. An example of a suitable material for the shunt 13 is a Mn'Zn-ferrite composed on Fe O MnCO and ZnO combined in the ratio of 50:27:23 by mol%. In this case, when the permanent magnet 12 is fitted to the recess in the temperature-responsive shunt 13, one side of the permanent magnet 12 and its periphery are covered with the magnetic material of the shunt 13.

With such an arrangement, since the permeability of the magnetic material of the shunt 13 is high when temperature is low, the magnetic flux that originates in the permanent magnet 12 is almost completely shunted by the magnetic material of the shunt 13, with the result that the magnetic flux density of the external magnetic field of the magnetic device 11 is low. However, when the temperature becomes high, the permeability of the magnetic material of the shunt 13 is reduced, with the result that the magnetic flux density of the external magnetic field produced by the magnetic device 11 becomes high due to the fact that the magnetic flux from the magnet 12 is less shunted by the magnetic material of the shunt 13. Accordingly, it will be understood that the flux density of the external magnetic field from the magnetic device 11 increases as the temperature increases.

It is not necessary that the permanent magnet 12 and the temperature-responsive shunt 13 used in the device 11 be limited to the configurations mentioned above. They can be formed, for example, with rectangular perimeters with one side of the permanent magnet and its rectangular perimeter covered by the magnetic material. Other polygonal forms may also be used.

As shown in FIGS. 3 and 4, the magnetic structure 17 according to the present invention uses two magnetic devices 11a and 11b attached to opposite ends of a strap, or bridge, of material having relatively high magnetic permeability, for example, or silicon steel a nickel-iron alloy known as Pe'rmalloy. The magnetic devices 11a and 11b are attached so that they extend beyond the ends of the strap 18 and have their respective magnets facing away from the strap. In addition, the flat sides 16a and 16b are, as shown in FIG. 4, aligned with each other so that the north and south poles N and S of both of the devices 11a and 11b are also aligned. The right-hand end of the strap 18 as shown in FIG. 4 is polarized to have a north magnetic pole and the lefthand end of the strap 18 is polarized to have a south magnetic pole. The magnetic flux within the strap 18 is thus additive rather than in bucking arrangement.

FIG. shows a magnetic flux field 19 representative of the structure 17. As may be seen, the central part of the field lines 19 between the two magnetic devices 11a and 11b is pulled inwardly toward the strap 18, whereas the flux at the ends extends outwardly. It has been further controlled by varying the amount of overlap of the relatively high permeability strap 18 with respect to the magnetic devices 11a and 11b. FIGS. 6 and 7 show two different overlapping amounts. In FIG. 6, the strap 18 overlaps relatively little of the magnetic device 11a, whereas in FIG. 7 the strap 18 overlaps a substantial part of the magnetic device 11a. The area, or portion, of the magnetic device 11a that is not overlapped by the strap 18, is indicated by the dimension W. In F IG. 6 where the overlap is relatively small, the length w is relatively large. The reverse is true in the structure shown in FIG. 7.

Since the permeability of the strap 18 is relatively high, the greater the overlap, that is the smaller dimension W, the more of the flux flows internally through the strap 18 and the less there is to form the field indicated in FIG. 6 by the lines 19a and in FIG. 7 by the lines 19b. Controlling the dimension W provides a very useful way of controlling the intensity of the magnetic field used to prevent mislanding, since the intensity of the field can be varied while keeping the temperatureresponsive devices 11a and 11b in firm, heatconductive relationship with the wall of the cathode ray tube that is to be controlled.

FIGS. 8 and 9 show, respectively, side elevational and rear elevational views of a cathode ray tube in which temperature-responsive magnetic structures of the type shown in FIGS. 3-7 are used. Just behind the face and within the funnel of the tube is a beamseparating structure in the form of an aperture mask or a grille of a standard type (not shown). A deflection yoke 24 is positioned on the neck 22 adjacent the funnel of the tube 21 to deflect electrons from electron gun means (not shown) within the neck to trace out a suitable raster on the face 23.

A typical position for the temperatureresponsive magnetic structures 17 and 170 on the funnel of the tube 21 is shown in FIGS. 8 and 9. The structures 17 and 17a are affixed to the funnel to be responsive to heat generated by electrons striking the internal beamseparating structure. Increasing the heat increases the amount of flux external to the structures 17 and 17A. This external flux is the flux that affects the trajectories of the electron beams within the tube to direct them at the appropriate points to produce correct landing of the electrons on the face 23. Since the tube 21 is constructed as a symmetrical device, it is advantageous that the structures 17 and 17a be arranged so that each of them has two magnetic devices. These are the devices lla and 11b in the case of the magnetic structure 17 and the devices 110 and 11d in the case of the magnetic structure 17a. Different amounts of overlap producing different dimensions W may be required to result in magnetic fields of the proper location and strength. As may be seen, the temperature-responsive magnetic devices Ila-11d are located farthest from the axis of the neck 22 and are in the correct positions to provide the most intense magnetic field at the corners of the screen 23.

The magnetic structures 17 and 17a are designed so that they do not adversely affect the trajectories of the found that this field configuration is particularly useful electron beams when the tube 21 is cold. As the tube heats up, the shunting effect of the temperatureresponsive shunt 13 of each magnetic device 11 is reduced automatically, thereby allowing more flux to extend into the tube 21 and produce greater effect on the beam trajectories, thereby compensating for the mislanding due to differential thermal expansion of the beam-separating structure and the color phosphor elements on the screen 23.

What is claimed is:

1. In combination with a color cathode ray tube having an envelope with a screen at one end thereof composed of arrays of different color phosphors, and in which electron beams are made to scan said screen for impingement on the respective color phosphors thereof; an arrangement for correcting temperature induced mislanding of said electron beams in respect to said respective color phosphors comprising elongated strap means of relatively high magnetic permeability, and temperature-responsive magnetic flux generating means attached to the opposite ends of said strap means and being effective to produce magnetic fields which vary in intensity with varying temperature and which are spread by said strap means, said strap means and magnetic flux generating means being disposed against said envelope of the cathode ray tube so that said magnetic flux generating means are influenced by the temperature of said tube and said magnetic fields act within the latter on said electron beams for correcting said temperature induced mislanding thereof.

2. The combination according to claim 1; in which said strap means includes two straps of said relatively high magnetic permeability and each having said magnetic flux generating means attached to said opposite ends-thereof, said envelope has a funnel-shaped portion leading to said screen, and said two straps and the respective magnetic flux generating means are disposed on said funnel-shaped portion at opposite sides of the center of the tube with said straps extending substantially normal to the line scanning direction of said beams.

3. The combination according to claim 1; in which a portion of each of said magnetic flux generating means extends beyond the respective end of said strap means.

4. The combination according to claim 1; in which said strap means is of silicon steel.

5. The combination according to claim 1; in which said strap means is of Permalloy.

6. The combination according to claim 1; in which each of said magnetic flux generating means includes a permanent magnet having north and south poles disposed at opposed portions thereof, and a shunt member attached to the respective end of said strap means and in which said permanent magnet is mounted so that the permanent magnets of said magnetic flux generating means at the opposite ends of said strap means have their north and south poles, respectively, directed toward each other; and in which each said shunt member is of a material having its magnetic permeability varied with changes in temperature.

7. The combination according to claim 6; in which each said permanent magnet has a non-circular periphery to which the locations of said north and south poles have a predetermined relationship, and each said shunt member has a recess shaped to receive the respective permanent magnet and to ensure the proper positional relationship of said poles of the magnets in said magnetic flux generating means at the opposite ends of said strap means.

8. The combination according to claim 6; in which said north and south poles of the magnets which are directed toward each other are in overlapping relation to the respective ends of said strap means, and the other poles of said magnets project beyond said respective ends of the strap means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 873 877 Dated March 25, 1975 I t- Hiromasa Machida, Hiroshi I chigaya and Kietsu Iwabuchi It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, change:

[30]- Foreign Application Priority Date NOV. 20, 1972 Japan ..47-13353 Nov. 20, 1972 Japan .47-133533 Signed and Scalcd this A ttest:

RUTH C. MASON C. MARSHALL DANN Atrestmg Officer (ommissiuner oj'Patents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,873,877 Dated March 25, 1975 lnventofls) Hiromasa Machida, Hiroshi Ichigaya and Kietsu Iwabuchi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading, change:

[30] Foreign Application Priority Date Nov. 20, 1972 Japan ..47-13353 Nov. 20, 1972 Japan ..47-133533 Signed and Scalcd this twent -third y December 1975 A ttes t:

RUTII C. M A SON C. MARSHALL DANN Arresting Officer Commissioner oflatenls and Trademarks 

1. In combination with a color cathode ray tube having an envelope with a screen at one end thereof composed of arrays of different color phosphors, and in which electron beams are made to scan said screen for impingement on the respective color phosphors thereof; an arrangement for correcting temperature induced mislanding of said electron beams in respect to said respective color phosphors comprising elongated strap means of relatively high magnetic permeability, and temperature-responsive magnetic flux generating means attached to the opposite ends of said strap means and being effective to produce magnetic fields which vary in intensity with varying temperature and which are spread by said strap means, said strap means and magnetic flux generating means being disposed against said envelope of the cathode ray tube so that said magnetic flux generating means are influenced by the temperature of said tube and said magnetic fields act within the latter on said electron beams for correcting said temperature induced mislanding thereof.
 2. The Combination according to claim 1; in which said strap means includes two straps of said relatively high magnetic permeability and each having said magnetic flux generating means attached to said opposite ends thereof, said envelope has a funnel-shaped portion leading to said screen, and said two straps and the respective magnetic flux generating means are disposed on said funnel-shaped portion at opposite sides of the center of the tube with said straps extending substantially normal to the line scanning direction of said beams.
 3. The combination according to claim 1; in which a portion of each of said magnetic flux generating means extends beyond the respective end of said strap means.
 4. The combination according to claim 1; in which said strap means is of silicon steel.
 5. The combination according to claim 1; in which said strap means is of Permalloy.
 6. The combination according to claim 1; in which each of said magnetic flux generating means includes a permanent magnet having north and south poles disposed at opposed portions thereof, and a shunt member attached to the respective end of said strap means and in which said permanent magnet is mounted so that the permanent magnets of said magnetic flux generating means at the opposite ends of said strap means have their north and south poles, respectively, directed toward each other; and in which each said shunt member is of a material having its magnetic permeability varied with changes in temperature.
 7. The combination according to claim 6; in which each said permanent magnet has a non-circular periphery to which the locations of said north and south poles have a predetermined relationship, and each said shunt member has a recess shaped to receive the respective permanent magnet and to ensure the proper positional relationship of said poles of the magnets in said magnetic flux generating means at the opposite ends of said strap means.
 8. The combination according to claim 6; in which said north and south poles of the magnets which are directed toward each other are in overlapping relation to the respective ends of said strap means, and the other poles of said magnets project beyond said respective ends of the strap means. 